1. Field of the Invention
The present invention pertains to (i) a drive device having slip stoppers that reliably prevent skewed movement of or damage to a belt, and more particularly, to a fusing device, used in an image forming apparatus such as a printer or a copying machine using the electrophotographic method, which has slip stoppers that prevent skewed movement of the fusing belt used for the heat-pressure fusing, or (ii) a transfer device, used in an image forming apparatus such as a printer or a copying machine using the electrophotographic method, that has slip stoppers that prevent skewed movement of the transfer belt.
2. Description of the Related Art
In a drive device that drives a belt, skewed movement of the belt easily occurs due to misalignment of the drive axes that drive the belt. Skewed movement of a belt may cause various problems in the belt drive device.
For example, image forming apparatuses such as printers or copying machines using the electrophotographic process are equipped with a fusing device that fuses the unfused toner image held onto a sheet, i.e., a recording medium. While various fusing methods are available, the heat-pressure fusing method is generally used. The fusing device using this heat-pressure method may be of a belt type or a heat roller type depending on the specific form of the rotatable member. Japanese Laid-Open Patent Application Hei 6-318001 discloses one example of a fusing device of the belt type.
A belt-type fusing device such as the one disclosed in said patent application (Hei 6-318001) has a drive roller and a heat roller having a built-in heat source, as well as a fusing belt that moves while being suspended over the pair of rollers, and the fusing belt is heated to a certain temperature by means of the heat from the heat roller. In this belt-type fusing device, the unfused toner on the sheet is conveyed such that it faces the fusing belt, and therefore, it is preheated by means of the radiating heat from the fusing belt before it reaches the nipping area where the fusing belt and the pressure roller are in pressure contact. As a result, the temperature at the nipping area may be set lower in a belt-type fusing device than in the roller fusing method, which makes fusing devices of this type more compatible with the demand for reduced energy consumption and quick printing. Further, since the toner is not melted to an unnecessary extent because the nipping area temperature can be set relatively low, the advantage is obtained that the amount of the releasing agent (such as silicone oil) that is used to prevent the transfer of the toner to the fusing belt, i.e., the offset phenomenon, may be reduced to one tenth of what is needed in the roller fusing method.
On the other hand, however, in belt-type fusing devices, if the fusing belt that is suspended between the rollers moves in a skewed fashion, the fusing belt may become damaged, or image noise may occur in the fused image.
The same problem exists in the transfer device that transfers the developed toner image held on the photoreceptor, which is the image carrier, in image forming apparatuses such as printers or copying machines using the electrophotographic method. In other words, the transfer device transfers the toner image from the photoreceptor to the transfer belt surface or the surface of a recording medium such as copy paper that is held on the transfer belt. When this is done, if the transfer belt moves in a skewed fashion, the image is transferred to a position that is offset from the initial targeted position, making accurate transfer impossible, or the transfer belt comes into contact with various components of the image forming apparatus, causing damage to the transfer belt.